A typical fuel pumping system for an aero-engine comprises a low pressure (LP) pumping stage operable to draw fuel from a fuel tank, and supplying the fuel at boosted pressure to the inlet of a high pressure (HP) pumping stage. The inter-stage flow between LP and HP pumping stages is typically used to cool engine lubrication oil in a fuel/oil heat exchanger.
Commonly, the LP pumping stage comprises a centrifugal impeller pump whilst the HP pumping stage comprises a positive displacement pump in the form of a twin pinion gear pump.
However, another option is to use two centrifugal stages in series. For example, EP A 0657651 describes an arrangement in which a first centrifugal pump acts as the LP stage, and a second centrifugal pump acts as the HP stage, the two pumps being cantilever-mounted to respective ends of a journal shaft driven by a drive shaft.